Design and analysis of the optical properties of electrostatic unipotential lens (einzel lens)

In the present paper, the geometrical and optical object properties of a unipotential electrostatic lens (einzel lens) are designed and analyzed using the Electron Optical Design program; this program uses the finite element method (FEM) as a basic numerical method. The effect of the distance between the three electrodes ( D e ) and the optical axis, the distance between the first and third electrodes with the middle electrode ( d e1 , d e2 ), and the width of the medial electrode ( W e ) of the lens are all studied for the best optical properties. It was found that the optical properties of the lens improved significantly with decreasing distance between the electrodes and the width of the center electrode of this lens. Upon our study, it was found that the best features are achieved when the lens length ( L e = 20 mm ), the distance between the electrodes (d e1 = d e2 = 4 mm), the axial distance ( D e = 3 mm), and the center electrode width ( W e = 5 mm), at constant energy ( P e = 5000 V). Here, ( C s = 88.84167 mm), ( C c = 12.84094 mm), ( f o = 15.4209 mm), ( C s / f o = 5.7611) and ( C c / f o = 0.8326).